Purification of metals



Patented Nov. 14 1939 PURIFICATION OF METALS Louis S. Deitz, Jr., Westiield, N. J., assignor to Nassau Smelting 85' Refining Company, Incorporated, New York, N. Y., a corporation of New York No Drawing. Application August 14, 1937, Serial No. 159,070

'1 Claims.

This invention relates to the purification of metals, and particularly to the removal of undesirable ingredients in the form of residual impurities from commercially pure alloys suitable for extrusion and casting purposes.

Where it is desirable to produce castings having smooth surfaces or to make extruded articles, such as cable sheaths, collapsible tubes, etc., the presence of relatively small amounts of undesirable ingredients in the form of residual impurities in the ordinary commercially pure metals employed sometimes interferes with the 'casting and extruding operations. These ingredients may be metallic or may consist of chemical compounds, such as oxides, sulphides, etc. At any rate, it has been found that the substantially complete removal of these ingredients results in the production of alloys of superior quality which produce clean castings and smooth extruded shapes.

The objects of the invention are to supply metals of more than ordinary purity, particularly purified casting and extrusion metals, and to provide simple, inexpensive and effective methods of producing such metals.

It has been found that when molten alloys consisting principally of lead or of tin or a mixture of lead and tin such as have been hitherto prepared commercially for casting and extrusion purposes, containing admixtures ofsuch metals as antimony or copper or both, are cooled, small amounts of insoluble compounds of a complex nature are produced. These compounds have heretofore been regarded as unimportant and negligible in their effect on the physical characteristics of the metal; but it has been discovered, in accordance with the present invention, that a marked and unanticipated improvement is produced in the metal if insoluble material thus formed be removed. While these compounds are chiefly metallic and probably consist of complex alloys which may contain lead, antimony, copper and tin, they may also comprise non-metallic compounds such as oxides, sulphides, etc. Since the insoluble compounds are usually lighter than the molten metal, they rise to the surface and may be skimmed off mechanically. Of course, if the compounds are heavier than the. metal, they may be removed by dec'a tation or other suitable procedure. The compou ds which are skimmed off are frequently harder than the alloy itself, and may even be sufliciently hard to be described as abrasive. Hence, the substantially complete removal of these compounds from the alloy produces a metal which is far superior to the usual commercial product used for extrusion operations, and for casting operations such as the production of slush" castings where a smooth surface is desired. It hasbeen found that tin alloys maybe purified in a similar manner.

The amount of material removed from the melt in accordance with the invention to remove residual impurities will depend to a large extent upon) the previous history of the alloy being treated. When the process of the invention is practised upon alloys which have been carefully purified to provide materials which are considered to be commercial pure and which would normally be used without further treatment to make castings, extruded shapes, bearings, etc., the quantity of material removed to eliminate these impurities would ordinarily not exceed about 0.5% of the melt and would usually be from 0.2% to 0.4% thereof. In any event, the amount of material removed from the melt would not materially exceed about 1% and the composition of the alloy treated is substantially unchanged by the purification treatment.

In accordance with the invention, a metal or alloy to be purified is heated to a temperature well above its melting point, and cooled, preferably slowly and with stirring, to the lowest temperature at which it can be cast into pigs or bars. All drosses which appear on top of the molten metal at that temperature are skimmed oil and the metal is cast into pigs or bars of convenient shape and size, or reheated for use.

A complete understanding of the invention will be obtained from the following detailed description of specific embodiments thereof which are given by way of example to illustrate the invention,

Lead-antimony alloys which may contain from approximately 1% to 15% antimony are frequently used for the manufacture of extruded articles, such as cable sheaths, collapsible tubes, etc., and are also employed in the manufacture of castings. Some of these alloys, also may contain quantities of tin. It has been found thatwhen such alloys are melted either from pigs of the correct composition or by adding the individual ingredients to a kettle so as to produce the desired alloy of the customary commercial purity therein, and are then cooled to a temperature which is substantially as low as that at which the alloy can be cast into pigs, substantially all the insoluble ingredients in the metal rise to the surface and may be skimmed off. This temperature varies for the different alloys, but cooling to the temperature within the range of 600 F. to 650 F., which is most suitable for the particular alloy, before skimming has proved to be satisfactory for lead-antimony alloys of this type.

This process has also proved to be effective in the treatment of tin alloys of the type used in the manufacture of inexpensive jewelry, such as is sometimes designated costume jewelry.

' Such alloys consist essentially of approximately 99% tin and 1% copper, and may contain relatively small quantities (less than /2% each) of other metals such as lead, antimony and bismuth. When such metals prepared in the usual manner are melted and the analysis has been found to be correct, it may be cooled to a temperature of approximately 600 F., the dross then removed and the alloy cast into bars. The purified metal will give bright and clean castings of the intricate shapes employed in the manufacture of inexpensive jewelry.

The process embodying the invention has also been found to be equally effective in the production of pure Babbitt metals. The skimming temperature to be employed will, of course, depend upon the composition of the Babbitt metal. However, the following table provides a practical guide to the temperatures which may be employed for the skimming operation:

Composition in percent skimming Alloy No. temperature Sn Sb Cu Pb In practicing the invention to purify one of these Babbitt metals the commercially pure molten metal is cooled to the temperature shown in this table for the metal having an analysis which is closest to that of the metal being treated, the dross is skimmed from the surface of the molten metal and the metal is cast into suitable bars or pigs. The resulting Babbitt metal is substantially free from the undesirable hard and abrasive materials which are frequently found in the usual Babbitt metals of commerce.

By skimming any of the various types of alloys described above at a temperature as low as that at which it may be subsequently cast into pigs or bars, alloys are produced which contain a minimum of the insoluble ingredients which interfere with the proper working of the metal. This temperature is usually, if not always, lower than the one at which it is subsequently used in industry. In consequence, those ingredients which would melt at the temperature at which the alloy is used but which would solidify before the metal does and thus cause difiiculties, are eliminated.

While the invention has been described as applicable to certain specific types of alloys, it is, of course, obvious that the invention may be used in the purification of any type of metal or alloy which will produce insoluble compounds on cooling that may be removed by such operations as skimming, decanting, etc.

While the process would usually be pr c ced by the refiner who produces the metal in bulk, the invention may also be employed with equal success by the ultimate user of the metal. The commercially pure metals in pig form containing residual traces of undesirable ingredients may be melted, cooled down to a temperature just above the freezing temperature thereof, and the dross skimmed off, after which the metal may be reheated to a temperature sufficiently high to employ it in casting operations for pouring into the cylinder of an extrusion press.

It will be obvious from the foregoing description that this invention provides metals and al loys of improved quality by effective methods which are bothsimple and inexpensive.

It is to be understood that wherever the term "metal is used herein, or in the annexed claims, it is intended to mean not only a single metal but also alloys containing two or more individual methods.

What is claimed is:

1. A process of treating a commercially pure alloy consisting of upwards of 80% of metal from the group lead and tin to remove residual abrasive impurities which tend to cause surface irregularities in finished products made therefrom while maintaining the composition of the alloy substantially unaltered, said alloy being one which would normally be used at temperatures well above its freezing point without further purification for the manufacture of slush castings, extruded shapes, bearings and the like, which process comprises heating such an alloy to a temperature at which all of its constituents are molten and which approximates that at which it will be employed in the manufacture of said products, cooling the alloy to a temperature substantially lower than that at which it is initially heated and lower than that at which it will be employed in the manufacture of said products, removing the small quantity of insoluble material produced, and reheating the alloy to a temperature suitable for its intended use.

2. A process of treating a commercially pure alloy comprising upwards of 80% of metal from the group lead and tin and which may contain metal from the group antimony and copper to remove residual abrasive impurities which tend to cause surface irregularities in finished products made therefrom while maintaining the composition of the alloy substantially unaltered, said alloy being one which would normally be used without further purification for the manufacture of slush castings, extruded shapes, bearings and the like, which process comprises heating such an alloy to a temperature well above its melting point, cooling the alloy to substantially the lowest temperature at which it can be cast into pigs whereby a quantity of insoluble material not exceeding about 0.5% of the original melt is produced, removing the insoluble material produced, and reheating the alloy to a temperature suitable for its intended use.

3. A process of treating a commercially pure alloy comprising from about 83% to about 99% of metal from the group lead and tin and from about 17% to about 1% of metal from the group antimony and copper to remove residual impurities which tend to cause surface irregularities in finished products made therefrom while maintaining the composition of the alloy substantially unaltered, said alloy being one which would normally be used without further purification for the manufacture of slush castings, extruded shapes, bearings and the like, which process comprises heating an alloy to a temperature well above its melting point, cooling the alloy to substantially the lowest temperature at which it can be cast into pigs whereby a quantity of insoluble material not exceeding about 0.5% of the original melt is produced, removing the insoluble material produced, and reheating the alloy to a temperature suitable for its intended use.

4. A process of treating a commercially pure lead-antimony alloy comprising from about 1% to about of antimony to remove residual abrasive impurities which tend to cause surface irregularities in finished products made therefrom while maintaining the composition of the 5 alloy substantially unaltered, said alloy being one which would normally be used without further purification for the manufacture of slush castings, extruded shapes, bearings and the like, which process comprises heating such an alloy to a temperature above 650 F., cooling the alloy to substantially 650 F. whereby a quantity of insoluble material not exceeding about 0.5% of the original melt is produced, removing the insoluble material produced, and reheating the alloy to a temperature suitable-for its intended use.

5. A process of treating a commercially pure alloy comprising about 99% of tin and about 1% of copper to remove residual abrasive impur- 50 ities which tend to Icause surface irregularities infinished products made therefrom while maintaining the composition of the alloysubstantially unaltered, said alloy being one which would normally be used without further purification 5 for the manufacture of slush castings, extruded shapes, bearings and the like, which process comprises heating such an alloy to a temperature above 600 F., cooling the alloy to substantially 600 F. whereby a quantity of insoluble material not exceeding about 0.5% of the original melt is produced, removing the insoluble material produced, and reheating the alloy to a temperature suitable for its intended use.

6. A process of treating a commercially pure alloy containing from 0% to about 91% of tin, from about 4% to about 15% of antimony, from about 1% to about 9% of copper and from 0% to about 90% of lead to remove residual abrasive impurities which tend to cause surface irregu- 5o larities in finished products made therefrom while maintaining the composition of the alloy substantially unaltered, said alloy being one which would normally be-used without further,

purification for the manufacture of slush castings, extruded shapes, bearings and the like, which process comprises heating such an alloy to a temperature well above its melting point, cooling the alloy to substantially the lowest temperature at which it can be cast into pigs, removing the small quantity of insoluble material produced, and reheating the alloy to a temperature suitable for'its intended use.

'7. A process of treating a commercially pure alloy containing from 0% to about 91% of tin, from about 4% to about 15% of antimony, from about 1% to about 9% of copperand from 0% to about 90% of lead to remove residual abrasive impurities which tend to cause surface irregularities in finished products made therefrom while maintaining the composition of the alloy substantially unaltered, said alloy being one which would normally be used without further purification for the manufacture of slush castings, extruded shapes, bearings and the like, which process comprises heating such an alloy to a temperature well above its melting point, cooling the alloy to substantially the temperature shown in the following table:

Composition in percent skimming Alloy No. temperature,

Sn Sb Cu Irb for the metal having an analysis which is closest to that of the metal being treated whereby a quantity of insoluble dross not exceeding about 0.5% of the original melt is produced, skimming off the resulting dross. and reheating the alloy to a temperature suitable for its intended use.

LOUIS S. DEITZ, Ja. 

